1. Field of the Invention
The present invention relates generally to telecommunications systems and methods for positioning a mobile station within a cellular network, and specifically to offering location services in parallel to other existing services for mobile stations capable of handling data communications.
2. Background and Objects of the Present Invention
Cellular telecommunications is one of the fastest growing and most demanding telecommunications applications ever. Today it represents a large and continuously increasing percentage of all new telephone subscriptions around the world. A standardization group, European Telecommunications Standards Institute (ETSI), was established in 1982 to formulate the specifications for the Global System for Mobile Communication (GSM) digital mobile cellular radio system.
With reference now to FIG. 1 of the drawings, there is illustrated a GSM Public Land Mobile Network (PLMN), such as cellular network 10, which in turn is composed of a plurality of areas 12, each with a Mobile Switching Center (MSC) 14 and an integrated Visitor Location Register (VLR) 16 therein. The MSC 14 provides a circuit switched connection of speech and signaling information between the MS 20 and the PLMN 10. The MSC/VLR areas 12, in turn, include a plurality of Location Areas (LA) 18, which are defined as that part of a given MSC/VLR area 12 in which a mobile station (MS) (terminal) 20 may move freely without having to send update location information to the MSC/VLR area 12 that controls the LA 18. Each Location Area 18 is divided into a number of cells 22. Mobile Station (MS) 20 is the physical equipment, e.g., a car phone or other portable phone, used by mobile subscribers to communicate with the cellular network 10, each other, and users outside the subscribed network, both wireline and wireless.
The MSC 14 is in communication with at least one Base Station Controller (BSC) 23, which, in turn, is in contact with at least one Base Transceiver Station (BTS) 24. The BTS is the physical equipment, illustrated for simplicity as a radio tower, that provides radio coverage to the cell 22 for which it is responsible. It should be understood that the BSC 23 may be connected to several BTS's 24, and may be implemented as a stand-alone node or integrated with the MSC 14. In either event, the BSC 23 and BTS 24 components, as a whole, are generally referred to as a Base Station System (BSS) 25.
With further reference to FIG. 1, the PLMN Service Area or cellular network 10 includes a Home Location Register (HLR) 26, which is a database maintaining all subscriber information, e.g., user profiles, current location information, International Mobile Subscriber Identity (IMSI) numbers, and other administrative information, for subscribers registered within that PLMN 10. The HLR 26 may be co-located with a given MSC 14, integrated with the MSC 14, or alternatively can service multiple MSCs 14, the latter of which is illustrated in FIG. 1.
A Serving General Packet Radio Service Support Node (SGSN) 30, which is part of the General Packet Radio Service (GPRS) architecture, connects with the MSC 14 to provide packet switching of high and low speed data and signaling in an efficient manner to and from the MS 20. When the MS 20 is engaged in a data call, e.g., the MS 20 has an Internet connection (not shown) for sending and receiving data, data is sent from the MS 20 to the SGSN 30. The SGSN 30 provides a packet-switched connection for the data. Received data is transmitted from the SGSN 30 to the MS 20.
Determining the geographical position of an MS 20 within a cellular network 10 has recently become important for a wide range of applications. For example, location services (LCS) may be used by transport and taxi companies to determine the location of their vehicles. In addition, for emergency calls, e.g., 911 calls, the exact location of the MS 20 may be extremely important to the outcome of the emergency situation. Furthermore, LCS can be used to determine the location of a stolen car, for the detection of home zone calls, which are charged at a lower rate, for the detection of hot spots for micro cells, or for the subscriber to determine, for example, the nearest gas station, restaurant, or hospital, e.g., "Where am I" service.
Circuit switched paging and identification of the MS 20 when the MS 20 is both IMSI and GPRS attached, e.g., registered with both the VLR 16 and the GPRS 30, is performed via the SGSN 30 instead of the MSC 14, due to the higher efficiency and capacity offered by the SGSN 30 as compared with the MSC 14. For similar reasons, it is more efficient to locate an MS 20 that is both IMSI and GPRS attached via the SGSN 30 rather than the MSC 14.
Currently, when an MS 20, which is registered with the SGSN 30, is being positioned, the MS 20 is not always able to make or receive data calls or send or receive short messages. With reference now to FIG. 2 of the drawings, using the Open Systems Interconnection (OSI) model, which was developed by the International Standards Organization (ISO) in 1982, the inability of the MS 20 to engage in other activities involving the SGSN 30 while being positioned can be explained by describing the connection between the MS 20 and the SGSN 30 as several functional layers arranged in hierarchical form. These consist of the physical layer 205, the data link layer 210 and the application layer 215, which are on both the SGSN 30 and the MS 20. The application layer 215 is composed of three sublayers: a Radio Link Control (RLC) sublayer 220, a Logical Link Control (LLC) sub-layer 225 and a Connection Management (CM) sub-layer 230, which is the highest sub-layer within the application layer 215.
The CM protocol 235 controls two separate transaction types: session management (SS layer) 232, which handles data call delivery, such as activating, modifying and deleting the contents of packet data protocols, and short message handling delivery (SM layer) 234, which handles the delivery of Short Message Service (SMS) messages. Each transaction type 232 and 234 can be allocated a separate Service Access Point Identifier (SAPI) 233 and 235, respectively, within the LLC sub-layer 225 for distinguishing between the transaction types 232 and 234. Alternatively, when a common LLC SAPI is used between different transaction types 232 and 234, it is possible for a mobile subscriber to establish two CM-connections 230, using the same LLC-connection 220, by using different protocol discriminators (PDs) (not shown) to distinguish between the transaction types. Therefore, it is possible to provide SMS and data call services at one time and to change between the different services if necessary.
Any transaction may be established in parallel to any combination of other transactions. However, for a given RLC-connection 220, LLC-connections 230 can only be established once for each of the transaction types 232 and 234. Thus, only one LLC-connection 230 is allowed at a time per transaction type 232 and 234. That implies that, if LCS were to be defined as part of either the SS layer 232 or SM layer 234, it would be impossible to offer an LCS transaction at the same time as another transaction if both transactions belonged to the same transaction type (SS 232 or SM 234).
It is, therefore, an object of the present invention to allow LCS transactions to be performed in parallel to other existing transactions such as data calls or short messages within a GPRS architecture.